An air inlet valve of the type defined above is generally known in the trade and has been found to operate in a highly satisfactory manner. The air inlet valve itself is of relatively small size, and has a diaphragm diameter of about 5 mm. Its individual parts are permanently secured to one another.
Already known from German Patent No. 1 299 165 is an air inlet valve for a milking cup in which the valve itself is secured to a head portion of the rubber teat cup so as to periodically admit air under atmospheric pressure to the head portion of the rubber teat cup. A valve chamber communicates with the atmosphere through a first passage, with a pulsator through a second passage and with the head cavity of the rubber teat cup through a third passage, and contains a valve body in the form, for instance, of a ball or a cylinder. During operation of a valve of this type, as a vacuum is generated in the pulsator passage, the valve body is aspirated against the action of gravity toward the outlet end of the pulsator passage and simultaneously obstructs the latter passage and the third passage which communicates with the head cavity of the rubber teat cup. As the vacuum subsequently disappears, the valve body finally drops down under the force of gravity, whereby the passage leading to the head cavity of the teat cup is opened, permitting atmospheric air to enter the teat cup through this passage from the exterior of the valve. Due to the inertia of the valve body, valves of this type operate relatively sluggishly and without properly defined opening and closing times. In addition, the atmospheric air admitted to the head portion of the rubber teat cup is not readily capable of promoting the draining of the milk body located below the teat because the teat, at least in its tightly full state, completely closes the suction nozzle of the teat cup so as to at least strongly retard the passage of air therethrough.
Known from German Offenlegungsschrift No. 16 32 935 is an air inlet valve which includes a valve member in the form of a diaphragm having one side exposed to atmospheric air while the other side communicates with the pulsator cavity of a milking cup via a passage opening through the valve seat surface. In addition, the side of the diaphragm facing toward the pulsator cavity communicates with the interior of the head cavity of a rubber teat cup via a further connecting passage. As soon as a vacuum is created within the pulsator cavity, the communication between the pulsator cavity and the interior of the head cavity of the teat cup is interrupted. As the pressure within the pulsator cavity subsequently rises to atmospheric pressure, the diaphragm is lifted from the valve seat, permitting air under atmospheric pressure to enter the head cavity of the rubber teat cup from the pulsator cavity through the connecting passage. Valves of this type suffer from substantially the same disadvantages as the valves already discussed.
German Offenlegungsschrift No. 20 46 276 discloses a further diaphragm air inlet valve, in which the region on one side of the diaphragm communicates with the pulsator cavity of a milking cup, while the region on the other side of the diaphragm carries a valve poppet which, in response to the position of the diaphragm, can permit and obstruct the entry of atmospheric air from the exterior of the milking cup via a passage communicating with the head cavity of the rubber teat cup.
Known from U.S. Pat. No. 3,255,732 is an air inlet valve in which an air inlet passage communicates directly via the milking cup with the suction nozzle of the rubber teat cup at a location below the teat. The air inlet passage is adapted to be selectively closed and opened to the atmosphere by a diaphragm valve controlled in response to the pulsator pressure. This control is carried out in such a manner that the presence of a vacuum in the pulsator results in atmospheric air being admitted to the suction nozzle of the rubber teat cup, while the presence of atmospheric pressure in the pulsator results in the connecting passage being closed so as to obstruct the flow of atmospheric air to the suction nozzle of the rubber teat cup. As a result, atmospheric air is always admitted to the suction nozzle of the rubber teat cup at the beginning of and during the suction cycle.
German Patent No. 1 274 847 discloses an air inlet valve in which the lower end of the milking cup is provided with a clamping member for clamping the lower end of the suction nozzle of the rubber teat cup, which is in the form of a gabled roof surface. The oblique and downwardly extending opposite faces of the gabled portion are formed with openings which communicate with the milk drain conduit. These openings are closed by the rubber teat cup when the latter is in its collapsed state, namely when the pressure within the pulsator passage is somewhat higher than that in the milk drain conduit. In this state, however, the collapsed rubber teat cup uncovers openings which are formed in the lateral end walls of the clamping member and communicate with the exterior, namely with air under atmospheric pressure. As a result, atmospheric air is admitted in this state to the suction nozzle below the teat. During the suction cycle, when the pulsator pressure substantially equals the milking vacuum, the rubber teat cup returns to its substantially tubular state, resulting in the milk drain passages of the clamping member being uncovered and the openings which communicate with the exterior being closed. A valve of this type suffers from the disadvantage, however, that its control is fully dependent on movements of the rubber teat cup. As a result, the control times may vary widely in response to the flow of milk. For example, in the case of a reduced milk flow, the control timing will be more extended, while in the case of increased milk flow, the control timing intervals will be shorter. In addition, a valve of this type does not operate abruptly, which is an essential prerequisite for optimizing the milking cycle, but opens and closes rather slowly. Further undesirable variations of the control timing are caused by aging of the rubber and the resultant loss of its elasticity.
A modified valve of the type discussed above has become known from German Gebrauchmuster No. 80 15 963.3. In contrast to the valve discussed above, this valve periodically opens and closes only the openings communicating with the exterior of the milking cup, that is with atmospheric air, while the space below the teat remains in constant communication with the milk drain conduit, so that the milk is continuously drained. In addition to the disadvantages set forth above, valves of this type suffer from the further disadvantage that milk may enter the air inlet passage, resulting in the danger that residual amounts of milk may remain in the passage, particularly towards the end of the milking operation. As these passages are very small, the cleaning thereof is rather difficult, and it frequently happens that milk coagulates in the air inlet passage without being noticed. If the entry of air is obstructed or reduced, the vacuum adjacent the tip of the teat tends to fluctuate in a completely uncontrolled and biotechnically undesirable manner, as will be discussed below with reference to FIG. 1 of the drawings. Thus, there exists an increased demand for a valve which is adapted to be readily cleaned or which can operate in such a manner that, if possible, the formation of residual milk deposits in the valve is prevented from occurring at all. A valve of this type would on the one hand ensure reliable operation under all practical conditions, and would on the other hand meet the strict cleanliness requirements which exist in the field of food processing.